Error when running stepwise regression

Question

I am trying to run a stepwise regression model. I keep receiving this message:

#Error in step(cdc.fit, direction = "backward") : 
#  number of rows in use has changed: remove missing values?
#In addition: There were 50 or more warnings (use warnings() to see the first 50)

Am I receiving this because of missing values?

Here is my code:

model=glm(health~
      ALCDAY5+
      AVEDRNK2+
      CHILDREN+
      CHKHEMO3+
      POORHLTH+
      BLOODCHOYes+
      BPHIGH4No+
      CHCOCNCRYes
      , data=data, fmaily=binomial)

 stepmodel_back <- model(cdc.fit,direction='backward') 
 summary(stepmodel_back) 

Thanks!

Answer 1

I've not used the stepAIC() function in MASS, but it looks like the following line is incorrect:

stepmodel_back <- step(cdc.fit, direction = "backward")

You've assigned your glm model to an object called 'model', but this line doesn't reference this object. Should it be:

stepmodel_back <- step(model, direction = "backward)

?

Hope this helps.